Introduction

The name "Sempervivum", literally translated, means
"always alive" and this is a reference to the hardiness
of most species. It is very difficult to kill them accidentally.
Rosettes left dry and without soil for several months, will usually
survive and grow rapidly as soon as suitable conditions are provided.

There are, however, a number of pests that will attack houseleeks
and, although their effects are not often lethal, they can spoil
the appearance of the plant and reduce its growth rate. The most
common pests are described below.

Insect pests

Vine Weevils (Otiorrhyncus sulcatus)

The larvae of vine weevils feed on the roots of houseleeks (and
other plants) mainly during the autumn, winter and spring. If
not checked, they eventually eat up through the stem of the rosette
until all that remains is a few detached leaves.

Vine weevil larvae

The larvae seem to prefer the large, smooth leafed varieties
to the hairy types and as the roots are eaten the plant becomes
detached from the soil and lies on the soil surface. The larvae
can often be found actually in the base of the plant but if not,
they will be found in the soil below. The simplest treatment is
to check each plant in the early spring and re-pot any that have
lost their roots. The larvae can then be found and destroyed.

For chemical control, a recently introduced insecticide called imidacloprid,
is claimed to give long-lasting protection against vine weevils and other pests
but we have not tried it ourselves. It is available under the trade name of
Provado.

A biological control method is available and sold under the
name of Nemasys. This is a culture of parasitic nematode worms
that attack and kill the vine weevil larvae. Nemasys is expensive
and best used for crops grown under glass although outdoor treatment
is now possible and may be worth trying if vine weevils are a
problem.

Adult vine weevils are about 10mm long and a greyish black
colour. There are no males and the females are mainly nocturnal
so not often seen. Adult females may sometimes be found crawling
on the ground around the plants where they are probably laying
eggs!

Root Mealy Bugs

Root mealy bug infestation

Plants infested with root mealy bugs grow very slowly or even
stop growing altogether if the infestation is heavy. Examination
of the roots of an infested plant will reveal the presence of
a bluish white, mould-like material that is secreted by the bugs
as they feed.

Mealy bugs are more often found on potted plants than on those
in open ground but they are not usually discovered until the plant
is re-potted. Once mealy bugs have been detected it is best to
remove all infested roots from the plant, then re-pot it in fresh
compost.

Pots which have held infested plants should be thoroughly cleaned
and disinfected before being used again. If mealy bug is a severe
problem it may be worth watering all plants with a systemic insecticide
once or twice during the growing season.

Aphids

Occasionally rosettes will be found infested with greenfly or
blackfly although populations of predators such as ladybirds will
reduce this problem. If necessary, plants can be sprayed with
a suitable insecticide. Infected plants may be marked for a while
but as new leaves grow they soon recover.

Diseases

It is rare to see houseleeks suffering from bacterial, virus or
fungus infections. Under damp growing conditions the occasional
rosette will rot away but this does not usually spread to other
plants. It is best to destroy any unhealthy looking plants, and
to make sure that the compost used is well drained. Normally no
other treatment is necessary.

Weeds

Most houseleeks should be kept outdoors even when grown in pots,
so weeds can be a problem. It is best to remove weed seedlings
as soon as they are seen and before they develop large roots or
start to shade the plants.

One common weed is Pearlwort. This has fine grass-like leaves
and small green or white flowers. Seedlings can easily be uprooted
but they are often so numerous that re-potting the plant in fresh
compost is the easiest treatment.

During the winter and spring the growth of moss can be a problem,
especially among the rosettes of smaller varieties. It is probably
easiest to remove moss by hand when the plant is re-potted.